In a typical cellular system, also referred to as a wireless communications network, wireless terminals, also known as mobile stations and/or User Equipments (UEs) communicate via a Radio Access Network (RAN) to one or more core networks. The wireless terminals can be mobile stations or user equipment units such as mobile telephones also known as “cellular” telephones, and laptops with wireless capability, e.g., mobile termination, and thus can be, for example, portable, pocket, hand-held, computer-comprised, or car-mounted mobile devices which communicate voice and/or data with radio access network.
The radio access network covers a geographical area which is divided into cell areas, with each cell area being served by a base station, e.g., a Radio Base Station (RBS), which in some networks is also called “NodeB” or “B node” and which in this document also is referred to as a base station. A cell is a geographical area where radio coverage is provided by the radio base station equipment at a base station site. Each cell is identified by an identity within the local radio area, which is broadcast in the cell. The base stations communicate over the air interface operating on radio frequencies with the user equipment units within range of the base stations.
In some versions of the radio access network, several base stations are typically connected, e.g., by landlines or microwave, to a Radio Network Controller (RNC). The radio network controller, also sometimes termed a Base Station Controller (BSC), supervises and coordinates various activities of the plural base stations connected thereto. The radio network controllers are typically connected to one or more core networks.
The Universal Mobile Telecommunications System (UMTS) is a third generation mobile communication system, which evolved from the Global System for Mobile Communications (GSM), and is intended to provide improved mobile communication services based on Wideband Code Division Multiple Access (WCDMA) access technology. UMTS Terrestrial Radio Access Network (UTRAN) is essentially a radio access network using wideband code division multiple access for user equipment units (UEs). The Third Generation Partnership Project (3GPP) has undertaken to evolve further the UTRAN and GSM based radio access network technologies. Long Term Evaluation (LTE) together with Evolved Packet Core (EPC) is the newest addition to the 3GPP family.
Mobility management is an important function in maintaining cellular networks. The goal of mobility management is to track where cellular phones, or User Equipments (UEs), are located in order for mobile phone services to be provided to the various UEs comprised in any given network. The network nodes which are primarily responsible for mobility management are the Mobility Management Entity (MME) and the Serving General Packet Radio Service (GPRS) Support Node (SGSN).
An important aspect of mobility management is handover. Handover is the process of transferring an ongoing call or data session from one channel connected to the core network to another. Handover is typically required when a mobile user is moving away from the area covered by one cell (e.g., a routing or tracking area) and entering the area covered by another cell.